International Increases in Merkel Cell Carcinoma Incidence Rates between 1997 and 2016.

Relatively little is known about the epidemiology of Merkel cell carcinoma (MCC) with regard to international trends in incidence, specifically relating to differences by age, sex, and anatomic site. We examined the trends in sex-specific incidence of MCC in the United States, Australia, New Zealand, Scotland, and Norway over a 20-year period (1997-2016) as well as the site-specific incidence trends in the United States. We used Joinpoint regression models to estimate the average annual percentage change in the incidence. In the total United States population, we observed an average annual percentage change of 2.7% (95% confidence interval [CI] = 2.0-3.3) for MCC, with sex-specific incidence increasing from 0.55 to 1.03 per 100,000 in men and from 0.28 to 0.45 per 100,000 in women. MCC incidence also increased in Queensland, Australia (average annual percentage change 1.8%, 95% CI = 0.7-2.8), New Zealand (2.0%, 95% CI = 0.4-3.7), Scotland (3.7%, 95% CI = 2.0-5.5), and Norway (4.0%, 95% CI = 2.1-5.9). In all populations, MCC incidence was higher in men than in women. Between 1993 and 2016 in the United States, the incidence of MCC of the head and neck and upper and lower limbs increased in both sexes. Despite being an uncommon malignancy, our analyses show that MCC incidence is steadily increasing both in areas of low and those of high ambient UVR levels.